In　this　work,　a　one-step　aptasensor　for　ultrasensitive　detection　of　homocysteine　(HCY)　is　developed　based　on　multifunctional　carbon　nanotubes,　which　is　magnetic　multi-walled　carbon　nanotubes　(Fe3O4@MWCNTs)　com-bined　with　the　aptamer　(Apt)　for　HCY　(Fe3O4@MWCNTs-Apt).　Fe3O4@MWCNTs-Apt　have　multiple　functions　as　follows.　(1)　Apt　immobilized　could　selectively　capture　all　target　molecules　HCY　in　the　sample;　(2)　Magnetic　Fe3O4　nanoparticles　could　separate　all　target　molecules　HCY　captured　by　Apt　from　the　sample　substrate　to　eliminate　the　background　interference　and　achieve　one-step　preparation　of　the　aptasensor;　And　(3),　MWCNTs　with　good　electrical　conductivity　become　a　new　electrode　surface,　construct　a　three-dimensional　electrode　surface　network,　make　the　electron　transfer　easier　and　thus　then　enhance　the　signal　response.　Results　show　that　there　is　a　good　linear　relationship　between　peak　current　of　square-wave　voltammetry　(SWV)　and　HCY　concen-tration　in　the　range　of　0.01　&　mu;mol/L-1　&　mu;mol/L,　with　a　limit　of　detection　(LOD)　0.002　&　mu;mol/L.　And,　selectivity,　reproducibility,　precision　and　accuracy　are　all　satisfactory.　In　addition,　it　could　be　applied　to　the　detection　of　HCY　in　the　plasma　of　lung　cancer　patients　successfully,　suggesting　that　this　one-step　aptasensor　for　HCY　has　a　potential　in　practical　clinical　applications.